The abundant secretion of type IIA secreted phospholipase A(2) (sPLA(2)) is a major feature of the inflammatory process of atherosclerosis. sPLA(2) is crucial for the development of inflammation, as it catalyses the production of lipid mediators and induces the proliferation of smooth muscle cells. We have analysed the activation of sPLA(2) transcription by cAMP and interleukin-1beta (IL-1beta), and shown that the 500 bp region upstream of the transcription start site of the rat sPLA(2) gene is implicated in activation by synergistically acting cAMP and IL-1beta. We transiently transfected and stimulated rat smooth muscle cells in primary culture and measured the promoter activities of serial and site-directed deletion mutants of sPLA(2)-luciferase constructs. A distal region, between -488 and -157 bp, bearing a CAAT/enhancer binding protein (C/EBP)-responsive element (-242 to -223) was sufficient for cAMP/protein kinase A-mediated sPLA(2) promoter activation. We find evidence for the first time that activation of the sPLA(2) promoter by IL-1beta requires activation of an Ets-responsive element in the -184 to -180 region of the distal promoter via the Ras pathway and a nuclear factor-kappaB site at positions -141 to -131 of the proximal promoter. We also used electrophoretic mobility shift assays to identify five binding sites for the Sp1 factor; a specific inhibitor of Sp1, mithramycin A, showed that this factor is crucial for the basal activity of the sPLA(2) promoter.

The inflammation that occurs during atherosclerosis is characterized by the release of large amounts of group IIA secretory phospholipase A2 (sPLA2-IIA). This study was designed to define the function of the three peroxisome proliferator-activated receptors (PPARs) on sPLA2 expression in vascular smooth muscle cells (VSMCs). We found that PPAR ligands decreased sPLA2-IIA activity and inhibited mRNA accumulation under inflammatory conditions. Furthermore, interleukin-1␤-induced sPLA2-IIA promoter activity was inhibited by the three PPAR ligands and in a similar way when cells were cotransfected with PPAR␣, PPAR␤, or PPAR␥, plus retinoid X receptor ␣ (RXR␣). Our study revealed that the regulation of sPLA2-IIA gene transcription by PPAR␣/RXR and PPAR␥/RXR heterodimers requires an interaction with a PPAR response element (PPRE) of the sPLA2-IIA promoter. In contrast, PPAR␤ operates through a PPRE-independent mechanism. In addition, we demonstrated that VSMCs expressed the transcriptional repressor BCL-6. Overexpression of BCL-6 markedly reduced sPLA2-IIA promoter activity in VSMCs, while a dominant negative form of BCL-6 abrogated sPLA2 repression by PPAR␤. The PPAR␤ agonist induced a BCL-6 binding to the sPLA2 promoter in VSMCs under inflammatory conditions. The knockdown of BCL-6 by short interfering RNA abolished the inhibitory effect of the PPAR␤ ligand on sPLA2 activity and prostaglandin E 2 release. Thus, the inhibition of sPLA2-IIA activity by PPAR␤ agonists may provide a promising approach to impacting the initiation and progression of atherosclerosis.The large family of phospholipase A2 (PLA2) enzymes hydrolyze ester bonds at the sn-2 position of glyceroacylphospholipids to produce lysophospholipids and nonesterified fatty acids such as arachidonic acid (C 20:4 [n-6]), the precursor of various proinflammatory lipid mediators, such as eicosanoids (37). To date there are four major families of PLA2. Several observations argue for the implication of type IIA secretory PLA2 (sPLA2-IIA) in the pathogenesis of various inflammatory diseases, including cancer, septic shock, rheumatoid arthritis, and atherosclerosis (38). The plasma of patients with various inflammatory diseases, particularly atherosclerosis, contains high concentrations of sPLA2-IIA (18). The synthesis of sPLA2-IIA is stimulated by inflammatory cytokines, such as interleukin-1␤ (IL-1␤), IL-6, and tumor necrosis factor alpha (TNF-␣) (2, 20). Moreover, sPLA2-IIA is largely expressed in vascular smooth muscle cells (VSMCs) (18) in response to proinflammatory cytokines produced by infiltrated macrophages. Overproduction of human sPLA2-IIA in transgenic mice contributes to atherogenesis (19). This enzyme catalyzes the production of precursors of lipid mediators (mainly prostaglandin E 2 [PGE2]), which in turn amplify the effect of cytokines on the dedifferentiation of VSMCs (11). The enzyme was reported to have other proatherogenic properties linked to its ability to hydrolyze phospholipid monolayers of high-and low-density lipoproteins (21). Previously...